[Godel_unicode]

You're changing units though, which in turn changes the outcome. The authors point was made about nutrients per volume, which is a rough approximation of how people actually eat food. While there are people who think "today I want 500kcal from beans and 75kcal from bananas..." they are relatively scarce.

When cast in units people actually do consider when eating (mass and volume) the authors point stands. Beef is more nutrient dense as a function of mass ~50kcal/, therefore you need a higher mass of plant matter to get equivalent nutrients.

Whether omnivores eat an equivalent mass of meat as vegetarians eat of plant matter is an interesting side question; I bet not.